Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$52.70	6.331%	$56.0364	$56.04	$56.05	$56.00
Purchase #2	$102.34	5.587%	$108.0577	$108.06	$108.05	$108.10
Purchase #3	$236.68	3.216%	$244.2916	$244.29	$244.30	$244.30
Purchase #4	$108.67	5.857%	$115.0348	$115.03	$115.05	$115.00
Purchase #5	$32.58	3.197%	$33.6216	$33.62	$33.60	$33.60
Purchase #6	$88.67	3.637%	$91.8949	$91.89	$91.90	$91.90
Purchase #7	$16.69	11.213%	$18.5614	$18.56	$18.55	$18.60
7 purchase totals =	$638.33		$667.4984	$667.49	$667.50	$667.50